FLIR systems are integrated into aircraft weapon systems for target location and target abatement. These systems are intended to increase the operational efficiency of the aircraft and lighten the burden on the pilot. A thermal image apparatus is an essential component of the FLIR system and generates a visible image on a TV-monitor (FLIR image) corresponding to the infrared radiation of the scene under observation. Hot targets with intense infrared radiation are thereby displayed as white while cold targets having lower infrared radiation are displayed as black.
The FLIR system is equipped with an automatic contrast and brightness control system for lessening the burden on the pilot. This system is intended to display scenes of special importance for the pilot that are below the horizon line so that they are displayed rich in contrast and with average brightness. This is achieved conventionally in that for the actual value formation of the contrast and brightness control, not the entire FLIR image is utilized; instead, only a horizontal strip-shaped segment (hereinafter referred to as evaluation window) is utilized. The upper boundary of the contrast and brightness window extends in the vicinity of the horizon line as it is visible in the normal flying position. On the other hand, the lower boundary lies at a distance away from the lower image edge such that the scenes that change rapidly because of the flying speed are not considered for the contrast and brightness control.
Disadvantages of conventional FLIR systems occur with intense roll movements of the aircraft wherein larger surfaces of the sky and smaller surfaces of the earth are imaged on the monitor than during normal flight. With the appearance of large black areas on the monitor, the automatic contrast and brightness control of the system becomes operational and reacts in that the contrast of the thermal image is attenuated and its brightness is increased which, in this case, provides a weak image having low contrast for the pilot.